I have used M1 since it came out back in the mid 1970's. Then, it was said to be good for one year or 25,000 miles. I took them at their word, and since then, I have did a one year OCI, regardless of the miles. Until I retired back in 2001, my yearly mileage was 18,000 to 20,000. My cars usually required a couple of quarts of makeup oil in 20,000 miles. Never, ever, had an engine issue.
Now, I am retired and 75 years old, and I drive about 9,000 miles a year. My 2005 Nissan Pathfinder, purchased new, does not require any oil addition in 9,000 miles. The owner's manual says it is OK to use 5W30, 10W30, or 10W40, with a preference for 5W30. For the last couple of years I have used M1 0W40.